Esterification process utilizing added unsaturated acids



Patented Mar. 17, 1953 ESTERIFICATION PROCESS UTILIZING ADDED UNSATURATED ACIDS Samuel B. Robison and John Rehner, Jr., Westfield, N. J., assignors to Standard Oil Development Company, a corporation of Delaware No Drawing. Application March 6, 1951,

Serial No. 214,212 a This invention relates to improvements in the methods of esterifying synthetic alcohols. More particularly, this invention relates to improved methods of esterifying synthetic branched chain alcohols of the C6 to C11 range by incorporating in the esterification reaction mixture small amounts of unsaturated aliphatic dicarboxylic acid derivatives.

The ever expanding use of plastic materials such as vinyl chloride polymers or copolymers, polyvinyl acetate, cellulose esters, acrylate and methacrylate resins, rubbers such as the emulsion copolymers of butadiene with styrene or acrylonitrile, or the copolymers of isobutylene with small amounts of a diolefin such as isoprene, have created a large demand for suitable plasticizers. ganic acid esters and particularly alkyl phthalic acid esters and more particularly di-2-ethy1- hexyl phthalate, have been known to be satisfactory plasticizers for the aforementioned high molecular weight plastic materials.

Synthetic branched chain x0 alcohol products produced by the well-known Oxo process (see e. g. U. S. Patent 2,327,066 and U. S. Bureau of Mines Publication R1 4270, Critical Review of Chemistry of the Oxo Synthetic, etc. 1948) have also come into commercial use in the production of esters suitable for plasticizers, by reaction with both aromatic and saturated aliphatic acids or anhydrides including such examples as phthalic acid, sebacic acid, stearic acid, lauric acid and adipic acid. Certain of the synthetic alcohols prepared by the oxonation and hydrogenation reaction are known to be especially suitable for the manufacture of ester plasticizers and, particularly, for use in clear plastics. These includ alcohols of from C4 to C12 range, such as the butyl alcohols, the octanols, and the nonanols with the C6 and C11 alcohols preferable. It has recently been learned that synthetic alcohols of the Ca series, and particularly those chosen from the iso-octyl type, are among the best type of esterification alcohols to prepare plasticizers, especially the phthalic acid esters.

It is essential that these esters have good color, 1. e., a relative absence of color so as not to color the clear resins. This latter criterion is difiicult of realization, however, probably because of complex impurities present in the synthetic alcohols which ar difiicult to ascertain. It is particularly difiicult to obtain esters of the color desired from an acid catalyzed esterification process, a process which has proven very satisfactory except for the excessive ester color. process are usually excessively colored and, hence, unsuitable for use as plasticizers for clear resins.

Normal and branched chain alkyl ora;

The esters from this 12 Claims. (omen-475') It has now been found that these difliculties in the acid catalyzed esterification reaction between aromatic and saturated aliphatic carboxylic organic acids or their derivatives, and especially phthalic acid, and the indicated synthetic alcohols are completely overcome by the addition of small amounts of unsaturated aliphatic dicarboxylic acid derivatives to the esterification reaction mixture. The resulting esters have distinctly less color and, hence, are vastly superior to those esters obtained from similar acid cata- 2 lyzed processes which do not utilize the agents of this invention.

The exact mechanism by which the unsaturated aliphatic dicarboxylic acid derivatives prevent the formation of undesirable color is not clearly understood. The impurities, probably present in the alcohols, which act as color formers are extremely complex in nature and probably include sulfur compounds. The active addition agents of this invention apparently operate by converting these color-forming bodies to innocuous matter.

Unsaturated aliphatic dicarboxylic acid derivatives utilized are illustrated by compounds such as the anhydrides, esters, acids, salts, etc., of the unsaturated dicarboxylic acids. Typical of these type compounds are:

Maleic acid Fumaric acid Ethyl hydrogen maleate Dimethyl maleate Dimethyl fumarate Diethyl maleate Diethyl fumarate Diisobutyl maleate Fumaryl chloride Fumaronitrile N-isobutylmaleimide Methylmaleic anhydride Itaconic anhydride Methylfumaric acid Dimethylmaleic anhydride The word, unsaturated, isemployed herein in its normal connotation, i. e., compounds containing carbon to carbon double bond linkages. Conversely, the term, saturated, indicates that the compounds so identified have no carbon to carbon double bond linkages. The term aliphatic dicarboxylic acid derivative is employed to connote those compounds which contain two groups or the anhydride structure resulting from the condensation of two carboxyl groups.

Particularly effective unsaturated aliphatic dicarboxylic acid derivatives are agents selected from the group consisting of anhydrides, esters and acids of an acid selected from the group consisting of maleic and fumaric acid. Especially effective and desirable agents are the maleic acid derivatives, e. g., maleic anhydride and esters such as diethyl maleate.

The alcohols for use in the indicated esterification reaction are preferably obtained by the OX0 process. The term, OX0 process, is well understood in the art as referring' to a process wherein an olefin feed is first reacted or oxonatecl with carbon monoxide and hydrogen at a temperature between 120 and 250 C., and under a pressure of about 150 to 400 atmospheres in the presence of a cobalt or similar catalyst, generally introduced in the form of a fatty acid salt, to form aldehydes in accordance with the following reaction:

The aldehydes so formed are then catalytically hydrogenated to form the desired alcohols as follows:

The preferred hydrogenation catalysts are those of the sulfur-sensitive nickel type though other known hydrogenation catalysts, such as the sulfides of nickel, molybdenum and cobalt, with or without support on carbon, silica, etc., can also be used, especially where a rugged sulfur-insensitive catalyst is desired.

The over-all carbonylation, or so-called Oxo reaction, as outlined above, provides a particularly effective method for preparing valuable primary alcohols, particularly of the C4 to C12 range, which finds large markets as intermediates for detergents and plasticizers. The C6 to C11 Oxo alcohol products are especially preferred for use in forming esters to be used as plasticizers in light-colored or colorless plastics and resins.

The most readily available olefinic feed stocks for the 0x0 reaction as outlined above are selected hydrocarbon streams derived from pctroleum refinery sources.'

In connection with the 0x0 reaction of olefin hydrocarbons, it has been found convenient to classify the various olefins into five fundamental types according to the character of carbon atoms linked by the olefinic bonds. These five types are as follows:

Type I CH2=CHR Type II RCH=CHR Type III CH2=C R Type IV RCH=C In the above formulas R represents a straight or a branched chain alkyl group, it being understood that where more than one symbol R appears in a formula, the several R symbols may represent the same alkyl group or different alkyl groups. Under this classification, for example, butene1, 3-ethyl pentene-l, or 4,4-dimethyl pentene 1 are Type I olefins; butene-2, 4,4-dimethyl pentene-Z, 2-methyl 5-ethyl hexene-3 are Type II olefins; 2,3,3-trimethyl butene-l is a Type III olefin; 2,4-dimethyl pentene-Z is a Type IV olefin; tetramethyl ethylene is a Type V olefin; and so forth.

In the 0x0 reactions, generally there is no invariable point of attack on the olefinic double bond such as one might predict from Markownikoifs rule, and thus in the case of Type I olefins of the formula H2C=CHCH2R, approximately equal amounts of both l-substituted alcohols of the formula CI-I2OH.CH2.CH2.CH2R and 2-substituted alcohols of the formula CH3 .CH (CH20H) .CH2R

are formed, with the 1-position being slightly favored. It is thus apparent that the 0x0 process is inherently committed to the production of at least some branched chain primary alcohols even when the starting material is a pure Type I straight chain olefin. Type V olefins are usually incapable of oxonation. The oxonation feed may contain mono-olefins of any type and suitable olefinic feeds may be fractionated, for example, from cracked gases, from Fischer-Tropsch synthesis products or from a polymerized stream of C3 to C5 olefins.

The alcohols formed by oxonation of the olefinic materials described above are naturally quite complex in character and the exact composition of many of these products is not known. The Ca 0x0 alcohols obtained have thus been found to comprise a mixture of isomers.

Studies have been carried out to elucidate ex- Type V perimentally the structural composition of these iso-octyl alcohol isomers. The combined techniques of cracking the stearic acid ester, analyzing the resulting olefins for type by infrared, hydrogenating and analyzing the resulting parafiins for individual components have been employed. Several conclusions can be drawn:

1. The isomers present comprise predominantly those having five and six carbon atoms in the longest straight chain.

2. To the extent of at least and probably or more, there are no alkyl groups in the 2-p-osition.

3. Of the possible 5% having one alkyl group in the 2-position, not more than about 1% based on the total alcohol, could be Z-ethyl h-exanol.

4. Not more than 10% (perhaps none) have 2-alkyl groups in the 2position.

5. Of the eleven possible isomers qualifying under (3) above, two cannot be formed through oxonation, and three are highly improbable on the basis of available compositional data on C7 polypropylene. The number of likely principal isomers is thus reduced to five.

The high Type I assay and the boiling range of the olefins derived from iso-octyl alcohol, together with a priori exclusion of 3,3-dialkylated alcohols as products of oxonation, limit the numher of possible major constituents of lso-octyl alcohol to nine isomers. On the basis of the best available data, only five of these alcohols could be formed in substantial amounts, the first three predominating.

Major Constituents of Typical Iso'Octyl Alcohol Alcohol B. P., '0. of Percent of Alcohol Total 4,5-Dimethyl hexanol 26 3,5-Din1ethy1 hexanoLfi 176 30 3,4-Dimethyl hexanol 18 3 and/or 5-n1ethyl heptanol 185. 8-186. 5 17 Miscellaneous and unidentified 9 I-Iydroxyl No. 429 Carbonyl No. l Saponification No. 0.5 Acid N0. 0.00l

A. S. T. M. distillation:

5% 175.3" C. 50% 183.3 C. 95% 188.3 C. Final 202.7 C.

(Recovery 99.0

Alcohol purity M, Theor. Hydroxyl No. (431) X 100 99.5%

and kinematic viscosity at 68 F., 12.4-12.8 centistokes. In general, it is desirable that the kinematic viscosity of the alcohol be between about 12.0 and 13.0 centistokes at 68 F.

Other synthetic branched chain alcohols, especially those in the C7 to C9 range such as 2-ethyl hexanol, can also be employed in the esterification reaction.

Since the aromatic and saturated aliphatic acids, anhydrides and similar derivatives may be interchangeably employed as reactants in the esterification reaction to achieve the same result in a similar manner, it is to be understood that the term, phthalic acid, or other organic acid also includes the anhydride, e. g., phthalic anhydride and the other similar derivatives. In a similar manner the term, alcohol, is to be understood to include other alcohol derivatives which can be employed in the esterification reaction to produce the identical esters.

The esterification process is carried out in the conventional manner for the acid catalyzed process except for the addition of the unsaturated aliphatic dicarboxylic acid derivatives. These esters and particularly the phthalic acid esters can thus be prepared by reacting the alcohol with acid, or with acid anhydride, or by first transforming the alcohol into an alkyl halide and then reacting the latter with a metal salt of the selected acid. For example, phthalate esters may be prepared efficiently by reacting about 2 mols of a suitable alcohol with one mol of phthalic anhydride in the presence of an acid catalyst, e. g., acid resins, sulfuric or an aromatic sulfonic acid catalyst, in an amount of from .01 to 1 weight per cent and using an aromatic solvent such as benzene, toluene, etc.

6 The esterification reaction is carried to substantial completion by esterification for a suflicient time. The unreacted alcohol is then stripped off fromthe ester product preferably manner except for the incorporation of the unsaturated aliphatic dicarboxylic acid derivatives in the reaction mixture. The iso-octyl phthalate ester itself boils at about 200220 C., at 2 mm. of mercury pressure. The reaction is carried out in corrosion-resistant equipment such as glasslined equipment.

It is desirable first to subject crude Oxo alcoho to a distillation at pot temperatures preferably not exceeding about 220 0., and preferably with previous caustic treatment, to remove some impurities such as aldehydes, acids, esters, acetals, unsaturated carbonyl compounds, etc.

In general, the preferred amount of unsaturated aliphatic dicarboxylic acid derivatives added to the esterification mixture is in the range of 0.1 to 5 weight percent, based on the reactants employed. The unsaturated aliphatic dicarboxylic acid derivatives may desirably be first dis-! solved in the alcohol employed or added directly to the reaction system.

This invention is illustrated by the following examples:

EXAMPLE I The efiect of adding of unsaturated aliphatic dicarboxylic acid derivatives to the esterification mixture of phthalic anhydride and an iso-octyl alcohol, prepared by the 0x0 process, was determined. Esterification reactions of identically similar reactants were carried out in the same manner as detailed above with the only variable being the addition of different amount of unsaturated aliphatic dioarboxylic acid derivatives.

The following table illustrates-the effectiveness of maleic anhydride and diethyl maleate in reducing the color of di-iso-octyl phthalate produced. These esters were all made in a toluene sulfonic acid catalyzed system. The efiect of concentration of maleic anhydride from 0.33 to 1.93 weight per cent on reactants is indicated.

Table I r Iso-Octanol (g.) 165 165 165 165 165 165 Phthalic Anhydride (g.) 94 94 94 94 94 94 Toluene Sulfomc Acid (g.) 0.26 0.26 0.26 0.26 0.26 0.26 Toluene (cc.) 20. 20 20 20 20 20 Maleic Anhydride (g 2. 60 1. 73 0.87 5.20 Di-ethyl Maleate (g.) 2. 60 Esterification Time (M 210 210 210 210 210 210 Hazen Color 25 40 40 50 25 EXAMPLE II The efiectiveness of adding a minor concentration of an unsaturated aliphatic dicarboxylic acid derivative in an acid catalyzed. esterification system which also had added thereto diphenylol propane as a deterioration inhibitor for standing life, was studied. The results follow in Table II.

It is apparent that the ester produced with 0.1

weight percent maleic anhydride had substantial color advantage over the product produced without this agent.

After finishing of the esters by stripping, washing, etc., the color build up of each was studied in an accelerated aging test in air at 300 C. 2

after a minor proportion of diphenylol propane had been added to each. Both esters exhibited no sensible color increase upon exposure to air at elevated temperatures indicating that the ester prepared by the process of this invention maintained its advantage. This shows in addition that the unsaturated aliphatic dicarboxylic acid derivatives do not 'deleteriously affect the functions of the deterioration inhibitors like diphenylol propane.

EXAMPLE H1 The iso-octyl phthalates made with various concentrations of maleic anhydride in the reaction system were evaluated as plasticizers for polyvinyl chloride. The evaluation data obtained are shown in Table III. The compounds were prepared with 50 parts by weight of plasticizer based on 100 of polyvinyl chloride. Compounds with and without diphenylol propane dissolved in the plasticizer were evaluated. In preparing the test vinyl blend samples, 100 gms. of poly vinyl chloride resin were dry-blended by hand with 1 gm. of lead stearate, gms. of plasticizer and 2 gms. of sodium organo phosphate (Vanstay 16). The results are tabulated in the table below.

Tensile properties were determined in the usual manner on 2. Scott Tester (model L-5) at about The results in Table III indicate that the plas diphenylol propane.

The improvement of ester color obtained through the process of this invention persists through the steam stripping operations of the ester.

The process of this invention is also applicable to the esterification of other C7-C9 branched alcohols such as Z-ethyl hexanol and yield similar but not as marked advantages. Other additives may be added to the esterification system as stabilizers for the esters such as diphenylol propane, 2,2-bis (4-hydroxy-5-methyl phenyl) propane, 2,2-bis (4-hydroxy-5-isopropyl phenyl) propane and his (2-hydroxy-5-chlorophenyl) methane.

The unsaturated dicarboxylic acid compounds also may be employed to remove undesirable color from esters which already have this color present.

It will be understood further that the foregoing examples have been given merely for purposes of illustration, but that other modifications of the present invention are possible without departin from the scope of the appended claims.

What is claimed is:

1. In a process for the preparation of an organic carboxylic acid ester from an organic carboxylic acid selected from the group consisting of unsubstituted monocyclic aromatic carboxylic acids and unsubstituted saturated aliphatic carboxylic acids and a synthetic branched saturated aliphatic monohydric unsubstituted alcohol employing an acid-type esterification catalyst, the improvement which comprises adding to the esterification mixture a minor proportion of an unsaturated aliphatic dicarboxylic acid compound.

2. In a process for the preparation of organic carboxylic acid esters from phthalic acid and synthetic branched chain saturated aliphatic monohydric unsubstituted OX0 alcohol in the presence of an acid-type esterification catalyst, the improvement which comprises carrying out the esterification in the presence of an unsaturated aliphatic dicarboxylic acid compound.

0 3. A process as in claim 2 in which the 0x0 alcohol is in the C6 to C11 range.

4. A process as in claim 3 in which the 0X0 alcohol employed comprises essentially as the major constituents 4,5-dimethyl hexanol, 3,5-dimethyl F., and 50 relative humidity, the rate of jaw hexanol, 3.4-dimethy1 e -met y1 heptanol separation being 20 inches per minute.

and 5-methyl heptanol.

Table III Maleic Anhydride, Percent e 1.0 1.0 0. 67 0.67

Ethyl Maleate, Percent Diphenylol Propane b Room Temperature Tensile Properies: v

Modulus 1, 860 l, 810

Tensile Strength. 3, 010 2, 940 2, 980 2, 940

Elongation 310 290 295 290 Aged 7 days 100 0 Modulus 100%... 2, 250 2, 240 2,310 2, 260

Tensile Strength 2, 940 2, 310 2, 880 2, 400

Elongation 270 160 205 165 Plasticizer Loss, Percent 16. 7 17. 7 16.6 17. 8

B Concentration present in weight percent on reactants during preparation of the di-iso-octylphthalate. b This is Weight percent of diphenylol propane dissolved in the ester prior to compounding 111 polyvinyl chloride. Complete evaluation recipe: Geon 101, 100 parts by weight; lead stearate plasticlzer, 50 parts by weight; and Vanstay l6, 2

parts by weight.

5. A process as in claim 4 in which the agent employed is maleic anhydride which is present n an amount of from 0.1 to 5 weight per cent based on the total reactants.

6. The process of claim 1 in which the aliphatic dicarboxylic acid compound is selected from the group consisting of aliphatic dicarboxylic acids, their esters and anhydrides.

7. The process of claim 6 in which the aliphatic dicarboxylic acid is maleic acid.

8. The process of claim 6 in which the aliphatic dicarboxylic acid is fumaric acid.

9. The process of claim 1 in which the acid yp esterification catalyst is toluene sulfonic acid.

No references cited. 

1. IN A PROCESS FOR THE PREPARATION OF AN ORGANIC CARBOXYLIC ACID ESTER FROM AN ORGANIC CARBOXYLIC ACID SELECTED FROM THE GROUP CONSISTING OF UNSUBSTITUTED MONOCYCLIC AROMATIC CARBOXYLIC ACIDS AND UNSUBSTITUTED SATURATED ALIPHATIC CARBOXYLIC ACIDS AND A SYNTHETIC BRANCHED SATURATED ALIPHATIC MONOHYDRIC UNSUBSTITUTED ALCOHOL EMPLOYING AN ACID-TYPE ESTERIFICATION CATALYST, THE IMPROVEMENT WHICH COMPRISES ADDING TO THE ESTERIFICATION MIXTURE A MINOR PROPORTION OF AN UNSATURATED ALIPHATIC DICARBOXYLIC ACID COMPOUND. 